Vertical sand mote molding machines are known which comprise a generally rectangular molding chamber in which the sand is introduced (for example, by blowing or by gravity), through a hopper or bell arranged at the upper part. Said chamber is closed by means of two closing elements or plates, namely, at one of the ends thereof, by means of a mobile and swiveling front plate to allow the exit of the molded mote, and at the opposite end by means of a rear plate associated with a compaction piston, which also serves to perform the pushing and corresponding expulsion of the mote.
The obtaining of the mote starts with the introduction of the sand in the molding chamber. Next, in a compression phase of the molding cycle, the sand is pressed by means of the opposing push of the front and rear plate. Then, in what can be called the extraction phase of the molding cycle, the front plate is opened and tilted to allow the exit of the mote, which is achieved by means of the push of the rear plate, thus causing the extraction of the mote from the molding chamber.
Machines of this type are described in, for example, U.S. Pat. No. 7,007,738 and U.S. Pat. No. 6,092,585. These patents describe vertical mote molding machines comprising a molding chamber which is closed by means of a shiftable and swiveling front plate and a rear plate provided at an end of an extraction piston, the mote being compacted by the opposing pressure of both plates. In this way, motes are obtained cyclically, which motes form two half-molds and, with the aid of the extraction piston, are expelled from the molding chamber, aligned and placed against one another forming a row which will shift along the corresponding work stations. Other examples of vertical mote molding machines are described in U.S. Pat. No. 4,442,882, EP-A-1101548, WO-A-01/12360 and EP-A-1219830.
For example, EP-A-1219830 describes a vertical mote molding machine in which, once the sand has been blown in the molding chamber, the pressing by means of the front and rear plates is performed by the opposing drive of two hydraulic cylinders, which push the front and rear plates to achieve the formation of the mote in the molding chamber. The drive of one of the cylinders, in a first direction, causes the shift of the rear plate for the compaction and extraction of the mote. The drive of the other cylinder occurs in a direction opposite that of the first cylinder, acting on a rear frame which, through a series of bars, is attached to the front plate, the shift of the front plate for the compaction and the tilting occurring.
Once the sand is introduced in the molding chamber, the mote is pressed by means of the opposing and simultaneous drive of the cylinder which pushes the rear plate and of the cylinder which pushes the front plate, thus achieving the formation of the mote in the molding chamber. Next, the cylinder of the front plate reverses its operation, causing the longitudinal outward shift of the frame and therefore, of the front plate. The cylinder of the rear plate continues its movement, facilitating the extraction of the mote. After that moment, if the shift of the front plate continues, a cam will swivel upwards, causing the push of a rod and therefore, the push and corresponding swiveling of the front plate. This swiveling is performed until the front plate is in a horizontal position at the upper part, in which situation the mote can be extracted by means of the push thereon by the rear plate, which is driven and longitudinally shifted by the cylinder of the rear plate.
Vertical mote molding machines are also known in which so-called “plunger cylinders” are used, which plunger cylinders are formed by two cylinders arranged coaxially and shiftable with respect to one another, such that to perform the compaction of the mote both cylinders act simultaneously, whereas to cause the extraction of the mote one of the cylinders shifts with respect to the other one.
Using hydraulic cylinders as devices for driving the closing plates, a good compaction of the mote is obtained. However, it has been considered that there are some drawbacks derived from using hydraulic cylinders such as, for example, a high maintenance cost, need for space to place the cylinders (something which considerably increases the size of the machine), a low precision in the movements of the cylinders, a high power consumption, etc.